An optical device having a micro lens array is disclosed in Japanese Patent Application Publication No. H06-194502. The device is manufactured with the following method shown in FIGS. 35A to 35D.
As shown in FIG. 35A, a photo-resist 101 is applied to a glass substrate 105. Then, the resist 101 is patterned into a predetermined pattern, as shown in FIG. 35B. Next, the resist 101 is annealed so that the resist 101 becomes to have a hemispherical shape. Here, the resist 101 is fluidized when the resist 101 is annealed at a certain temperature, so that the resist 101 is deformed to have the hemispherical shape because of a surface tension of the resist 101. Then, the resist 101 is cooled down to a room temperature, so that the resist 101 is solidified with having the hemispherical shape. In this way, the resist 101 is used as a construction of a micro lens array.
Further, another optical device having a micro lens array is manufactured with the following methods. A photo-resist on a glass substrate having a hemispherical shape like the resist 101 on the substrate 105 shown in FIG. 35D is prepared. Then, the resist with the substrate is etched with an anisotropic etching method such as a highly anisotropic dry-etching method, so that the hemispherical shape of the resist is transcribed to the substrate. Thus, the glass substrate has a hemispherical shape, and is used as a construction of a micro lens array.
However, in the above methods, a curvature of a lens, i.e., a curvature of the hemispherical shape of the resist 101 or the glass substrate 105 is not controlled correctly. That is because the hemispherical shape is formed by the surface tension of the resist 101. Therefore, the hemispherical shape is formed by natural consequences, so that the micro lens array having a controlled curvature is not manufactured in the above methods. Specifically, it is difficult to manufacture a lens having a small curvature radius i.e., a large numerical aperture (i.e., a large NA) with the above methods. Further, it is difficult to manufacture a lens having aspheric shape with the above methods.